1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a method and apparatus for transmitting data, and more particularly, to a method and apparatus for efficiently transmitting a data frame in a communication network.
2. Description of the Related Art
With the advent of ubiquitous networking and improvement in networks, studies have been carried out on various aspects of network technology. For example, a wireless network is advantageous because data is received and transmitted without using wires. However, when transmitting massive multimedia data, several apparatuses share and use the given wireless data resources. Accordingly, when competition between users is high, wireless data resources may be lost due to a collision of the wireless data resources during communication. Thus, the efficiency of the wireless network can be inferior compared to the efficiency of a wired network.
In order to reduce the number of collisions and loss of wireless data resources and to safely receive and transmit the wireless data resources, a wireless local area network (WLAN) uses a distributed coordination function (DCF) or a point coordination function (PCF), whereas a wireless personal area network (WPAN) uses a channel time allocation scheme.
Some problems of a wireless network can be solved by applying the above mentioned functions in the wireless network, but obstacles, such as multi-channel, fading, interference, etc., which interfere with the smooth reception/transmission of data still exist. Also, as the number of wireless networks increase, possibilities of a collision during data transmission and a loss of data increase. Accordingly, data needs to be re-transmitted, which adversely effects transmission speed in a wireless network. Specifically when a high quality of service (QoS) is required in order to transmit accurate data, such as audio/video data (A/V data), a method of re-transmitting data needs to be improved, for example, by reducing the number of re-transmissions, thereby securing available bandwidth as much as possible.
FIG. 1 is a diagram illustrating a frame transmission process in a conventional wireless network.
Referring to FIG. 1, in a conventional IEEE 802.11 standard based wireless network, a transmitter generates headers for each layer using a media access control (MAC) layer and a physical (PHY) layer, and transmits a PHY header (HDR), a MAC HDR, and a data frame formed of data 1 to a receiver. The receiver accurately receives the above information after a short inter frame space (SIFS) has passed, according to the conventional IEEE 802.11 standard. When the receiver is unable to detect any errors in the received information, the received information is sent to an upper layer. Also, in order to show that the information has been received, the receiver transmits an acknowledgement (ACK) frame formed of the PHY HDR, the MAC HDR, and an ACK 1.
The transmitter, after receiving the ACK frame, transmits a following data frame formed of the PHY HDR, the MAC HDR, and data 2 to a receiver, after a DCF inter frame space (DIFS) has passed according to conventional IEEE 802.11 standard.
FIG. 2 is a diagram illustrating a processing method when the transmission of a frame has failed when using a conventional method of transmitting a frame.
Referring to FIG. 2, a transmitter transmits a first frame including data 1 to a receiver. When data is successfully transmitted, the receiver transmits ACK 1 to the transmitter, as shown in FIG. 1, in order to confirm the successful data transmission and transmits data 1 to an upper layer of a MAC protocol. The transmitter which received ACK 1 then transmits a second frame including data 2 to the receiver. After transmitting the second frame, the transmitter starts a counter. When the counter stops and the transmitter has not received an ACK from the receiver for a period of time called ACK timeout, the transmitter regards that the transmission of data 2 failed, and so re-transmits the second frame to the receiver.
When the above process is repeated a predetermined <Retry Limit> number of times, but the receiver still has not responded, the transmitter skips data 2 and transmits a following data 3. The receiver, which received data 3, transmits data 3 to an upper layer when an error is not detected in data 3 and data 3 is received without any bug, and transmits ACK 3 to the transmitter.
As described, using the conventional method of transmitting a frame, unnecessary time is spent during the transmission of frames because whenever a transmitter transmits several frames, the transmitter needs to receive ACK frames for each frame. FIG. 3 is a diagram for describing problems in a conventional method of transmitting a frame.
As shown in FIG. 3, time is wasted because ACK frames have to be received for each data frame, data transmitting efficiency is low because the amount of data that needs to be transmitted is limited by a MAC HDR and a PHY HDR added to each frame, and a relatively big overhead is generated because of the MAC HDR and the PHY HDR when the length of a data that needs to be transmitted, such as A/V stream data, is small. For example, in the IEEE 802.11 standard, when a MPEG transport stream of 188 bytes is transmitted, the length of the MAC HDR included in the data frame is 30 bytes, and the time length of the PHY HDR is 20 μsec, thereby a bigger overhead is generated compared to data that is to be actually transmitted. Also, the problems become more serious as the number of re-transmissions increases. On the other hand, these problems not only occur in a wireless network, but also in similar communication networks, such as power line communication (PLC) networks, etc.